Abstract

A novel method for the spectropolarimetric measurement of materials using the channeled spectrum is described. A pair of high order retarders are incorporated into the illuminating optics of a broadband spectropolarimeter, so that the sample under measurement is illuminated with the light that is modulated in the spectral-dependence of its polarization. The Fourier analysis of the channeled spectrum obtained from the spectropolarimeter allows determining the four spectrally-resolved polarimetric parameters of the sample simultaneously. This approach has a feature that it requires neither mechanically- nor electrically-controllable components for polarization modulation, similar to the previous method for the channeled spectropolarimetry in which the high-order retarders are placed in the receiving optics. The new method can offer the same information about the sample as has been obtained by the previous method, provided that all the optical components satisfy the principle of reciprocity. Furthermore, the new method has an additional advantage over the previous method that it is less susceptible to the sample-induced fluctuations of the wavefront or ray-direction. The effectiveness of this method is experimentally demonstrated with the measurement of a birefringent sample.

Effects of the ray-bending introduced by the sample. The directions of the light ray passing through R1 and R2 change between the measurement and the calibration in the SP-CSPSA (a), but do not change in the SP-CSPSG (b).

Retardations of a thin quartz plate (TQP) plotted as a function of the wavenumber. Solid and broken curves are respectively obtained by the SP-CSPSG and the SP-CSPSA, and the dotted curve is the theoretical value based on the Sellmeier’s equation.

Fluctuations of the measured retardation of a TQP under the ray-direction variations. The three graphs are respectively taken at wavenumbers (a) 1.4 × 104 cm-1, (b) 1.6 × 104 cm-1, and (c) 1.8 × 104 cm-1.